A number of applications require an elongated article having the contradictory properties of resisting deformation by bending or twisting and yet of being able to withstand repeated flexing along its major axis. Among the more common applications are markers and barriers for traffic control which must be able to withstand being struck by this traffic. Such applications include highway delineator posts like those described in U.S. Pat. Nos. 4,245,922, 4,084,914, 4,298,292 and 4,343,567, gate arms for parking lots, and legs for highway barriers.
The two basic approaches have been unitary articles and mechanical composite articles. The former approach is illustrated in U.S. Pat. Nos. 3,380,428; 4,061,435; 4,123,183; 4,290,712; 4,297,050; 4,298,292; and 4,245,922. These designs often either do not withstand repeated flexing, particularly through 90.degree. along their major axis such as would occur if they were struck by vehicles or they have inadequate resistance to the wind or similar environmental sources of stress. For example, at column 4, lines 28-30 of the 4,298,292 patent acknowledge that ultimate failure upon flexing to be inevitable while the design of the 4,245,922 patent is unable to resist twisting in the wind.
The mechanical composite approach involves multipart assemblies which significantly increase the cost and complexity of these articles. This approach is illustrated in U.S. Pat. Nos. 1,939,968; 3,838,661; 4,004,545; 4,032,248; 4,105,350; 4,106,879; 4,126,403 and 4,343,567.
An interesting blending of the two concepts is illustrated in U.S. Pat. No. 4,084,914. A channel member similar to that illustrated in U.S. Pat. No. 4,245,922 is stiffened against bending or twisting in the wind by bolting a second channel to it. The two channels face each other rather than resting one in the other. The two channel members are preferably constructed of polycarbonate, a rigid thermoplastic material which can undergo substantial elastic deformation. The article requires assembly with bolts or other fasteners and it is not clear that it could withstand repeated 90.degree. deflections without suffering permanent damage.